can't execute the blender python through subprocess
First I expect you should use subprocess.run() rather than popen, which is a lower level call that offers more options that you aren't using.

I would suggest using a full path rather than the ./ prefix to a command.

The main source of your error is your arguments list, the first parameter to run() or popen() is called args and is the arguments used to run the external application. In your case you are passing the path to the current executable, which would be the python interpreter you are running the script in. The next argument is a single string, which python appears to be interpreting as a file path to a script to run.

The arg parameter should be a list of strings that you would use in a terminal, the first string is the executable and each following string would be each option passed to the executable.

By defining the list on multiple lines for clarity -

myargs = [
    "/home/abc/Destkop/blender/blender-2.78/blender",
    "-b",
    "/home/abc/Destkop/blender/car.model"
    ]
subprocess.run(myargs)


The full path can be made more flexible by using bpy.app.binary_path.

You also have a trailing space after the filename which would get interpreted as part of the filename.